Thin film transistors (TFTs) are widely used in liquid crystal display devices, organic electroluminescence (EL) display devices, etc.
Amorphous silicon TFTs used in large display devices have a mobility of about 1 cm2/V·s, can be formed by plasma CVD (Chemical Vapor Deposition), and therefore can be formed uniformly and inexpensively over a large surface area.
Low-temperature polysilicon TFTs used in small-to-mid-sized display devices have a mobility of about 100 cm2/V·s and have high reliability when operated for a long period of time.
In recent years, TFTs having higher reliability are desirable. Therefore, oxide semiconductors used as the semiconductor layer material of TFTs are drawing attention.